This invention relates to laser printing device, and more particularly to a laser printing device which is suitable for recording or printing images gradated in density, or having halftones (hereinafter referred to as "halftone images".
Heretofore, in order to record halftone images, a method is employed in which the intensity of a laser beam applied to an optical recording material is modified in an analog mode. However, the method is disadvantageous in that, when the optical recording material is employed which is low in the characteristic of gradation with respect to optical intensity, two-valued records, namely, black and white are excessively emphasized. This difficulty can be effectively eliminated by the employment of a halftone recording method in which the recording of an image is carried out substantially in a binary mode; that is, large dots are employed for black regions, and small dots are employed for gray regions the color of which is nearly white. In a conventional halftone forming system, a laser beam applied to an optical system is changed in position, to cause an aberration in the optical system thereby making the resultant light spot foggy. However, the method suffers from a difficulty that the relationship between the fogginess of the light spot and the laser beam's incident position is relatively low in linearity, and therefore it is difficult to record halftone images with high accuracy.